1. Field of the Invention
The present invention relates to a bonding machine for fabrication of a liquid crystal display, and, more particularly, to a stage structure in a bonding machine for fabricating a liquid crystal display (LCD) having the liquid crystal dropping method applied thereto, and a method for controlling a bonding machine.
2. Background of the Related Art
Keeping pace with development of an information oriented society, demands on displays increase gradually in a variety of forms, and, recently to meet the demands, different flat display panels, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), Vacuum Fluorescent Display (VFD), and the like, have been under development, and some of which are employed as displays in various apparatuses.
The LCDs have been used most widely as mobile displays while the LCD replaces the Cathode Ray Tube (CRT) owing to features and advantages of excellent picture quality, lightweight, thin, and low power consumption. Besides the mobile type LCDs, such as a notebook computer monitors, LCDs are under development for television (TVs) for receiving and displaying broadcasting signals, and monitors of computers.
Despite the various technical developments in the LCD for serving as a display in different fields, the efforts for enhancing a picture quality of the LCD as a display are inconsistent with the features and advantages of the LCD in many aspects. Therefore, for the LCD being employed in various fields as a general display, a key for development of the LCD lies in how much the LCD is made to implement a high quality picture, such as high definition and high luminance, and a large sized screen while the LCD is maintained to have the features of light weight, thin, and low power consumption.
The LCD may be fabricated by a generally known LCD injection method, in which one substrate having sealant coated thereon so as to form an injection hole is bonded to the other substrate under a vacuum, and liquid crystal is injected therein through the injection hole in the sealant, or by a liquid crystal dropping method. The liquid crystal dropping method is disclosed in Japanese Patent Laid Open Publication Nos. 2000-284295, and 2001-005405, in which one substrate having liquid crystal dropped thereon and the other substrate are provided, and the two substrates, placed oppositely in a vertical direction, are brought closer to bond the two substrates.
Of the two methods, the liquid crystal dropping method is advantageous in that many steps (such as the step of formation of the liquid crystal injection hole, the step of injection of liquid crystal, and the step of sealing the liquid crystal injection hole) can be omitted, and less equipment is required. Accordingly, studies for development of various apparatuses for use in the liquid crystal dropping method have been made.
FIGS. 1 and 2 illustrate a related art bonding machine having the liquid crystal dropping method applied thereto.
The related art bonding machine is provided with a frame 10 forming an outer shape, stage parts 21 and 22, a sealant outlet part (not shown), a liquid crystal dropping part 30, chamber parts 31 and 32, chamber moving means, and stage moving means.
The stage parts have an upper stage 21 and a lower stage 22, and there is an electro-static chuck 28 at a bottom the upper stage 21. The electro-static chuck 28, which is an insulating material plate having two rectangular recesses, each with a plate electrode built therein covered with a dielectric material of which main surface is on the same plane with a bottom surface of the electro-static chuck 28. Each of the buried plate electrodes (not shown) is connected to a positive/negative DC power through an appropriate switch. When a positive or a negative voltage is applied to the plate electrodes, a negative or positive charge is induced at the main surface of the dielectric material on the same plane with the bottom surface of the electro-static chuck 28, to adsorb the substrate by a Coulomb force generated between the substrate 51 and the transparent electrode film caused by the charge.
The sealant outlet part and the liquid crystal dropping part 30 is fitted to a side of a location at which the frame is bonded, and the chamber part has an upper chamber unit 31 and a lower chamber unit 32, detachable from each other.
The chamber moving means has a driving motor 40 for selective movement of the lower chamber unit 32 to a location the bonding is made, or to a location discharge of the sealant and dropping of the liquid crystal is made, and the stage moving means has a driving motor 50 for driving the upper stage 21 upward or downward, selectively.
The steps of a method for fabricating an LCD by using the foregoing related art bonding machine will be explained in detail.
First, the second substrate 52 is loaded on the lower stage 22 in the lower chamber unit, and the lower chamber unit 32 is moved toward a location the upper stage 21 is located by driving the driving motor 40 of the chamber moving means.
Under this state, the upper stage 21 produces a vacuum adsorbing force, and adsorbs the second substrate 52 by vacuum, and the lower chamber unit 32 is moved to a location for coating sealant and dropping liquid crystal by driving the driving motor 40.
Then, the first substrate 51 is brought into the lower stage 22, and, then, the lower stage 22 produces a vacuum adsorption force, and vacuum adsorbs the first substrate 51. This state is illustrated in FIG. 1.
Under this state, the lower chamber unit 32 having the lower stage 22 is moved to a location for coating sealant and dropping the liquid crystal by the chamber moving means 40.
Then, when the sealant coating and the liquid crystal dropping are finished by the sealant outlet part and the liquid crystal dropping part 30, the lower chamber unit 32 is moved to a location for bonding the substrates by the chamber moving means 40, again, as shown in FIG. 2.
Then, chamber units 31 and 32 are bonded by the chamber moving means 40, to close the spaces where the respective stages 21 and 22 are located respectively, and the spaces are evacuated by separate vacuum means. In this instance, the second substrate 52 vacuum adsorbed at the upper stage falls down onto a catch stop pawl (not shown), and the electro-static chuck 28, having a voltage applied thereto at a time the chamber is evacuated adequately, adsorbs the second substrate 52 on the catch stop pawl.
Then, the upper stage 21 is moved downward such that the second substrate 52 adsorbed at the upper stage 21 is brought into contact with, and pressed down to, the first substrate 51 adsorbed at the lower stage 22, to bond the substrates, thereby finishing fabrication of the LCD.
However, the foregoing related art assembler (bonding machine) has the following problems.
First, because the related art bonding machine has a system in which the sealant coating and the liquid crystal dropping are made on the substrate having the thin film transistors formed thereon, and the substrate having the color filter layer formed thereon, the related art bonding machine becomes bulky by the parts for carrying out the sealant coating and the liquid crystal dropping.
Particularly, the bonding machine for large sized LCDs required recently becomes more bulky, such that fabrication of the large sized LCDs is unfavorable.
Second, if the sealing in the coupling between the lower chamber unit and the upper chamber unit is not perfect, the substrates may be damaged during the bonding, and the bonding may be defective due to infiltration of air through a leakage part. Accordingly, parts for prevention of air leakage is additionally required in the vacuum state, and the required accuracy causes difficulty.
Third, the electro-static chuck of two plate electrodes, absorbing the substrate by having voltages of different poles applied thereto, are likely to drop the substrate as the electro-static absorbing force is not adequate. Moreover, the large sized glass substrate cannot be adsorbed.
Fourth, the alignment of the substrates by moving the lower chamber unit in a lateral direction in bonding the substrates is very difficult, which increases a time period required for the entire fabrication. That is, because there are many movements required for the fabrication, such as the movement of the lower chamber unit to a location for dropping the liquid crystal or coating the sealant onto a substrate held at the lower stage, and the returning of the lower chamber to a location for bonding the substrates again when above process is finished, accuracy of the substrate alignment cannot be secured.
Fifth, as explained, even if the power to the electro-static chuck 28 is cut off for separating the substrates from the upper/lower stages after the bonding is finished, the potential remaining between the upper stage and the bonded substrates may impede easy separation of the bonded substrates, which causes misalignment of the bonded substrates, and deterioration of adhesive force of the sealant.